Tabular grain emulsions have found a wide acceptance in the art of photography.
Tabular grains are herein defined as grains having two substantially parallel (111) crystal faces, each of which is substantially larger than any other single crystal face of the grain. The aspect ratio, that is the ratio of the diameter to thickness of the tabular grains is substantially greater than two.
In a radiographic element, spectrally sensitized tabular grain emulsions as compared to non-tabular grain emulsions having a comparable speed (sensitivity) and silver coverage, show an improved granularity, an increased silver image covering power especially for strongly hardened layers, a more rapid developability and a decreased dependence of the photographic results on changes of the processing temperature.
Besides these general advantages tabular grain emulsions, coated in double side coated radiographic materials, show an improved speed-cross-over relationship as set forth in U.S. Pat. No. 4,411,986.
Although double side coated radiographic elements containing spectrally sensitized tabular grains have numerous advantages an important disadvantage is met for tabular grains having a mean grain thickness of less than 0.3 .mu.m in that an increased dye stain of the fully processed radiographic elements can occur. This dye stain is the result of an incomplete removement of the spectral sensitizer during processing. Because of their high surface to volume ratio tabular grains contain significantly higher amounts of spectral sensitizer per volume of silver halide to obtain the optimal sensitivity and thus higher amounts of spectral sensitizer have to be removed.
Particularly with relation to recent trends as shorter processing times to save time, lower regeneration volumes with a composition that is less threatening the environment, it is important to offer suitable films to the customer that are adapted to the new requirements.
Solutions for the increased dye stain after processing have been described e.g. in EP-Application 426 193 and U.S. Pat. No. 4,960,683, wherein thiols, triazolium thiolates, disulphides and thioether compounds have been added to the processing solutions or to the photographic material. The addition of products to the layer(s) of the photographic material that are released during the processing of the said material are described in U.S. Pat. No. 5,108,888.
Another solution is offered by the choice of a spectral sensitizing dye with an adapted structure like benzimidazolo carbocyanines disclosed in EP-A 506 584. Other miscellaneous measures consist e.g. in the addition of very fine high silver iodide crystals to the protective coating capable of being dissolved during fixation as in U.S. Pat. No. 4,520,098.